A few years ago we bought 4 crowns of 2 different kinds of rhubarb and only one has really flourished although they have all had the same treatment. So sometimes the fault lies in the plant itself.
That said, rhubarb likes shade and water and being fed. I not only give ours manure each winter/spring, but also pour comfrey 'tea' on it regulary. This is made from steeping comfrey leaves in a lidded bucket. When it stinks its ready to be mixed with more water and given to plants. It is a great source of potash and loved by tomatoes, raspberries and rhubarb.
Sounds a great idea getting a crown from your mohter's clump.